Circuits for conversion of an input direct current voltage to an output direct current voltage at a different potential include a switching regulator type of DC-DC converter. This DC-DC converter includes a switching element that applies a direct current voltage from a direct current power supply to an inductor (coil) to allow a current to pass through and store energy in the inductor, a rectifier circuit that rectifies the current in the inductor in an energy emission period when the switching element is off, and a control circuit that turns on or off the switching element. The switching regulator type of DC-DC converter performs the following control: an error amplifier detects the level of an output voltage and feeds back the results to a pulse-width modulation (PWM) comparator; and the turn-on time of the switching element is extended in response to a drop in the output voltage whereas the turn-on time is shortened in response to a rise in the output voltage.
Some electronic devices, such as displays for automobiles, have recently used, for example, piezoelectric elements as actuators controlling the attitudes of components. Such a piezoelectric element has a capacitive load and is driven at a relatively high voltage. Thus, a differential amplifier may be used as a load-driving circuit for the piezoelectric element, and a switching regulator type of DC-DC converter having a high boosting rate may be used as a power supply for supplying a power voltage for the amplifier. Since batteries for automobiles have relatively large variations in voltage, it is expected to use a peak-current control scheme (current limit PFM scheme) for DC-DC converters or power supplies that generate power voltages for automobile electronic devices, where the peak current is kept constant regardless of the level of the voltage to be boosted.